Garrett AT Pro
Garrett AT Pro Depth Chart: Realistic Depth by Target and Soil
Quick answer
With the stock 8.5 by 11 coil in mild soil, a Garrett AT Pro typically gives a confident, identifiable signal on a coin at roughly 6 to 8 inches, a faint signal to around 10, and a large relic considerably deeper. Mineralised ground can cut all of those figures by a third or more.
Depth is the most exaggerated number in this hobby and the least transferable. A detector's reach depends on target size, target surface area, coil size, soil mineralisation, moisture, how long the object has been in the ground, and how hard you are willing to listen. Any single number quoted for the Garrett AT Pro without those conditions attached is decoration.
What follows are ranges, tied to a target, a coil and a soil condition. They describe a signal you would act on, not the absolute physical limit where a trace of a response might exist. The AT Pro target ID chart covers the related question of how deep the number stays honest, which is usually shallower than where the tone survives.
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Garrett AT Pro
The stock 8.5 by 11 DD coil and Pro mode proportional audio are what these depth ranges assume.
Price was accurate when this page was compiled and changes often.
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How deep does a Garrett AT Pro actually detect?
Read these as bands for a signal you would dig, using the stock 8.5 by 11 DD coil. Mild soil means low mineralisation inland ground. Mineralised means red clay, iron-rich soil or black sand.
A Garrett AT Pro with the stock coil typically gives a diggable coin signal at 6 to 8 inches in mild soil and 4 to 6 inches in mineralised ground, with large relics reaching 12 inches or more and small gold rarely past 4.
| Target | Mild soil | Mineralised soil | Comment |
|---|---|---|---|
| Small gold ring, under 2 grams | 2 to 4 in | 1 to 3 in | Low conductor, small surface area. The hardest target on the list |
| US nickel | 4 to 7 in | 3 to 5 in | The classic calibration target and a fair proxy for mid-size jewellery |
| US dime | 5 to 8 in | 4 to 6 in | Small but a good conductor, which partly compensates |
| US quarter | 6 to 9 in | 4 to 7 in | The figure most people quote when they say coin depth |
| Silver dollar or large silver | 8 to 11 in | 6 to 8 in | Surface area is doing the work here |
| Musket ball or large lead | 6 to 9 in | 5 to 7 in | Lead is a poor conductor but mass helps |
| Large iron relic, axe head or plate | 12 in or more | 8 to 12 in | All metal mode and a slow sweep are worth several inches |
| Modern can or large aluminium | 10 to 14 in | 8 to 11 in | Useful only as a reminder that size beats value on depth |
Ranges describe a repeatable, diggable signal rather than a faint trace at the edge of detection. Drawn from the depth behaviour AT Pro owners consistently report and from the general physics of single frequency VLF detection. No figure here is a Garrett specification.
Why is an air test always deeper than the field?
An air test removes the ground, and the ground is the problem. Swinging a coin past a coil in free air gives a number that has no soil mineralisation absorbing the signal, no moisture, no halo, no adjacent iron and no ground balance compromise. Air test figures for the AT Pro are routinely two to four inches optimistic compared with the same coin buried in average soil, and the gap widens as mineralisation rises.
Air tests are still useful for one thing: comparing two coils or two settings on the same machine on the same day. As an absolute measure of what you will find, they are worthless. The buried test plot described on the target ID chart page is the honest substitute, and it costs an afternoon.
How much depth does the coil change?
Less than people hope, and not always in the direction they want. Going from the stock coil to the larger NEL Hunter 12.5 by 8.5 typically buys an inch or two on coin-sized targets in clean ground and rather more on large objects, because a bigger coil illuminates more volume. Going down to the 5 by 8 sniper coil costs depth on paper and gains you finds in practice, because in dense trash the limiting factor is separation, not reach. The Mars Sniper 10 by 6 sits between the two.
The full fitment picture is on the AT Pro coil compatibility chart, and the coil size selector will put a recommendation against the site you are actually standing on.
What does soil mineralisation do to AT Pro depth?
Mineralised ground attenuates the transmitted field and adds its own signal, and the detector has to subtract that ground signal to see the target. The more it subtracts, the less sensitivity remains for the target. In practice, heavily mineralised red clay or black sand can cost a third of the depth available in mild soil, and it costs target ID accuracy first: the number goes unreliable at a shallower depth than the tone does.
Manual ground balancing buys some of that back, which is why the mineralised rows in the settings by site type table call for manual balancing and frequent rechecks. The Garrett AT Gold exists partly for this reason, with a ground balance window designed for exactly this ground.
How should you measure depth on your own ground?
Bury known targets at measured depths in your own soil, let the ground settle, and record which ones you can hear and which ones give a usable number. Do it again after rain. That single test will tell you more about your machine's real reach than every depth claim online combined, and it gives you a personal baseline to check against when you suspect a coil or a battery is failing. Newer detectorists should pair this with the intermediate setup, which covers the accessories that make the recovery half of the job tolerable.
Sources
- Garrett AT Pro owner's manual, ground balance and all metal mode sections
- Garrett AT Pro published specification sheet
- NEL Hunter 12.5 by 8.5 coil listing specifications for the AT Pro
Frequently asked questions
Can a Garrett AT Pro really detect 10 inches deep?
On a coin, only in favourable conditions. In mild, low mineral soil with a well ground balanced machine and a careful slow sweep, a large silver coin can produce a diggable signal around 8 to 11 inches. A dime at that depth is rare. In mineralised ground those numbers fall by a third. Large iron and large relics go considerably deeper because surface area drives detection.
Does a bigger coil make the AT Pro deeper?
On large targets, yes, noticeably. On coin-sized targets, a larger coil such as the NEL Hunter typically buys an inch or two in clean ground and can lose you finds in trash, because it sees several targets at once and averages them. Depth and separation trade against each other. The right coil is the one that matches the site rather than the one with the biggest number on the box.
Why does my target ID go wrong before the signal disappears?
Because identification needs a stronger signal than detection does. The machine can still hear a faint response at depths where it no longer has enough signal to classify the conductivity reliably, so the number wanders and usually drifts downward. A good rule is to trust the number for roughly the top two thirds of your depth range and treat deeper readings as tone information only.
How does wet ground affect AT Pro depth?
Moisture usually improves conductivity and can slightly increase depth in mild soil, which is why many detectorists prefer hunting after rain. On salt ground the opposite happens, because the salt itself becomes a competing conductor and forces lower sensitivity. Either way ground balance drifts when moisture changes, so rebalance rather than assuming yesterday settings still apply.
Do old coins really read deeper because of a halo?
Metal ions migrate into surrounding soil over decades and can make a long buried target appear larger to the detector, which is the halo effect. It is real for some metals in some soils, particularly iron and copper, and much weaker for others such as silver and gold. It is not a reliable depth bonus, and disturbing the soil around a target reduces it, so do not plan a hunt around it.
Researched, not professional advice. This page is compiled from published specifications, manuals and owner-review consensus, not hands-on testing. Target ID numbers, depth figures and settings vary with soil chemistry, moisture, target size, depth, orientation and firmware version, so treat every figure here as a starting point and verify it against your own machine's manual and your own ground. As an Amazon Associate we earn from qualifying purchases.